1. Technical Field
The embodiments herein generally relate to receiving electromagnetic waves, and, more particularly, to receiving electromagnetic waves using photonics.
2. Description of the Related Art
Radar along with its applications and uses are manifold. Invented in the 1940's and continually refined over the previous decades, radar continues to be the most useful and practical means for a host of applications including tracking aircraft and other aerial born objects. In the past, tracking of aerial targets, such as aircraft or missiles, has been achieved with basic or conventional radar. Types of radar used in the past included various types of Pulsed Doppler coupled with moving target indication receivers, inverse synthetic aperture radar, and radar ranging types of radars. The application of radar has typically been for the purpose of searching, tracking, selecting, and identifying sundry targets through the use of superheterodyne radar receivers. While the same radar equipment of the past are still commonly used today, today's equipment is now coupled with fast computers and digitizers that help to display information more accurately and accelerate data handling.
Problems with present radar and electronic warfare technologies include such issues as range inaccuracy, Doppler range ambiguity, fratricides (due to radar misinterpretation error), excessive clutter contamination and inter system interference, and low ballistic missile interception rate. These issues originate from superheterodyne down conversion, commonly used in conventional radio frequency receivers. In particular, superheterodyne down conversion requires numerous pulses for tracking targets. However, environments and practical conditions change with time. Numerous pulses lead to time average and blurring, a process that masks the pertinent information and contributes to the issues with conventional radio frequency receivers cited above.
For example, a conventional Pulsed Doppler radar receiver typically requires numerous transmitted pulses to achieve a correlation; however, radar targets continuously change their motions. The requirement of numerous pulses leads to motion blurring. In addition, due to motion blurring, target velocities become almost impossible to measure accurately and precisely. Moreover, the micro-Doppler signatures typically cannot be clearly and distinctively revealed by conventional radar systems. With micro-Doppler signatures, the pulses of interest are usually only instantaneously available. The complete and faithful digitization is almost impossible to achieve with the current limitations of conventional radio frequency receivers.
Other limitations of conventional radio frequency receivers include relying on higher speed and higher bandwidth capable technologies, relying on a higher number of bits in an analog-to-digital converter, and relying on faster processing digital electronics to improve overall performance. However, this approach to improve the overall performance of the receivers may reach a physical performance limit soon.